Literally:
however, what, you have, you hold on (to), until, ???, whenever, I shall
come.

How does hOU function here?

Mark, hello...Virgil Newkirk here.....

As you have made clear by a literal rendering of verse 25.....There is a
having by some....and an imperative...a charge if you will to put a tight
hold on it....then interestingly this is followed by not one, but two
genitives. This indicates that this having and holding onto is to be
characterized by...given qualification from...having the nature of whatever
is in the genitive.The genitive case signifies that the substantive is to
pass through...or has passed through and taken on...."whatever the genitive
is" The substantive takes on the distinction of ACRIS and hOU. Therefore hOU
is working here to give the having and holding the characteristic of "where"
they are to be holding on "at". hOU is an adverb of place.